U.S. patent application number 10/666999 was filed with the patent office on 2005-03-24 for stepped manifold array of microchannel heat sinks.
Invention is credited to Srinivasan, Raman, Treusch, Hans-Georg.
Application Number | 20050063433 10/666999 |
Document ID | / |
Family ID | 34313235 |
Filed Date | 2005-03-24 |
United States Patent
Application |
20050063433 |
Kind Code |
A1 |
Treusch, Hans-Georg ; et
al. |
March 24, 2005 |
Stepped manifold array of microchannel heat sinks
Abstract
An assembly for providing a concentrated, vertically stacked
array of laser beams from a horizontally offset array of
electrically serially-connected metallic microchannel heat sinks
each bearing a laser diode bar. The heat sinks are mounted on
horizontally offset planes of the manifold which has coolant
channels serving adjacent heat sinks that are separated from each
to increase the electrical resistance of the fluid path between
adjacent ones of said heat sinks. Stepped optical deflectors
re-arrange the horizontally emitted laser beams into vertical
stack.
Inventors: |
Treusch, Hans-Georg;
(Tucson, AZ) ; Srinivasan, Raman; (Tucson,
AZ) |
Correspondence
Address: |
Howard R. Popper
4436 E. Camelback Rd.
Phoenix
AZ
85018
US
|
Family ID: |
34313235 |
Appl. No.: |
10/666999 |
Filed: |
September 20, 2003 |
Current U.S.
Class: |
372/36 ; 372/34;
372/35 |
Current CPC
Class: |
H01S 5/02423 20130101;
H01S 5/024 20130101; H01S 5/4025 20130101 |
Class at
Publication: |
372/036 ;
372/035; 372/034 |
International
Class: |
H01S 003/04 |
Claims
What is claimed is:
1. A manifold for supplying a stack of metallic, microchannel heat
sinks each mounting a laser diode bar with coolant fluid, said heat
sinks forming part of series-connected electrical path, comprising:
an insulating body having a plurality of offset parallel planes for
mounting a respective plurality of said microchannel heat sinks;
said planes terminating coolant channels in fluid communication
with corresponding channels in said heat sinks; said coolant
channels communicating with adjacent ones of said heat sinks being
separated from each other by at least the width of one of said heat
sinks to increase the electrical resistance of said fluid path
between adjacent ones of said heat sinks.
2. A manifold according to claim 1 wherein said parallel planes are
minimally offset from each other so as to concentrate the optical
power emitted by said laser diode bars.
3. A series-connected stack of metallic, fluid-cooled microchannel
heat sinks each bearing a respective laser diode bar for emitting
optical power, an insulating body having a plurality of
horizontally offset parallel surfaces for mounting a respective one
of said heat sinks; said surfaces having coolant channels in fluid
communication with corresponding channels in said heat sinks; said
coolant channels communicating with adjacent ones of said heat
sinks being separated from each other by at least the width of one
of said heat sinks to increase the electrical resistance of said
fluid path between adjacent ones of said heat sinks; and a
plurality of optical reflective surfaces for deflecting the optical
power emitted by said laser bars into a plurality of vertically
stacked beams.
4. An assembly for providing a concentrated, vertically stacked
array of laser beams from a horizontally offset array of
electrically serially-connected metallic microchannel heat sinks
each bearing a laser diode bar, comprising: a coolant channel
bearing manifold having horizontally offset planes each mounting a
respective one of said heat sinks; the coolant channels serving
adjacent ones of said heat sinks being separated from one another
to increase the electrical resistance of the fluid path between
adjacent ones of said heat sinks; and a series of stepped optical
deflectors for re-arranging the laser beams emitted from the laser
diode bars into vertical stack.
5. An assembly according to claim 4 wherein said manifold is of
insulating material.
6. An assembly according to claim 5 wherein the coolant in said
cooling channels is water.
7. An assembly according to claim 5 wherein said stepped optical
deflectors are glass plates each having a beveled edge positioned
to receive the light output of a respective one of said laser
diodes.
Description
FIELD OF THE INVENTION
[0001] This invention relates to closely stacked arrays of
monolithic, edge-emitting laser diode bars mounted on microchannel
heat sinks for high power applications and, more particularly, to a
manifold for supplying metallic microchannel heat sinks with
coolant while reducing corrosion in the heat sinks.
BACKGROUND OF THE INVENTION
[0002] To obtain more optical power for industrial applications
than can be provided by a single laser bar, arrays of vertically or
horizontally stacked laser diode bars are typically required.
Because a typical laser bar emits on the order of tens of W of heat
in a very small volume, it is conventional practice to mount the
laser bar on a heat sink and, more particularly, on a water-cooled
microchannel heat sink whose copper channels offer a large surface
area for heat transfer to the cooling water. When laser diode bars
together with their microchannel heat sinks are vertically stacked
for greater optical power, they are usually connected electrically
in series. To connect the stack of laser bars in series, adjacent
heat sinks are separated by a layer of electrically insulating
material whose thickness is approximately the same as that of a
laser diode bar. In such arrangements, adjacent components are
placed as close together as possible to maximize the optical
intensity of the emitted light beams. However, the minimum spacing
between adjacent light beams emitted by the stack of laser bars is
determined by the thickness of the components and the heat
dissipating capacity of the stack. The best available separation
between adjacent components in the stack (or array), whether the
components are individual laser diodes or laser diode bars, is
about 1.2 mm which is capable of producing a power density of 200
watts/sq. cm.
[0003] It has heretofore been proposed in U.S. Pat. No. 5,987,043
to increase optical power density by employing a stack of heat
sinks having diode bars mounted at the ends of the heat sinks
instead of at the top edges of each so that adjacent emitted light
beams can be closer than the thickness of the heat sinks.
Alternatively, as shown in German patent DE 2,153,969 and Japanese
patent JP 4,426,789 each laser bar may be mounted on a respective
step of a shared, staircase like, water-cooled heat sink. In the
more recently-issued U.S. Pat. No. 6,229,831 a shared heat sink
having a triangular cross-section was employed together with a
triangular submount for each of the laser diode bars, the angle of
the submount complementing the angle of the triangular heat
sink.
[0004] Unfortunately, mounting a laser bar at the end of a
microchannel heat sink, as shown in FIG. 2 of the '043 patent, is
not as efficient from the standpoint of maximum heat transfer as
mounting the laser bar at the top edge of the heat sink.
Furthermore, vertically stacked arrays of serially-connected
microchannel heat sinks leads to unexpected corrosion problems in
the water path that reduce the effective life of the heat sink. On
the other hand, the '831 patent states that because of the
difficulty of manufacture, the use of microchannel heat sinks is
not possible with a "staircase" configured array of laser bars.
SUMMARY OF THE INVENTION
[0005] In accordance with the principles of the present invention,
a stair case array of copper microchannel heat sinks is made
possible by the use of an insulating manifold that provides a fluid
path between adjoining heat sinks that reduces corrosion of the
fluid paths in the heat sinks. The manifold has a series of
parallel, offset planes or steps each of which provides a fluid
connection to a respective microchannel heat sink each of which
advantageously may be of the type disclosed in U.S. Pat. No.
6,177,203, and which are commercially known as "Monsoon" heat sinks
marketed by the assignee of the present invention. The fluid
passages provided by the manifold between adjacent microchannel
heat sinks are longer than in a conventional, vertically stacked
array while the steps of the manifold permit the laser beams from
the diode bars on the heat sinks to be spaced more closely than is
possible with the conventional stacked array.
BRIEF DESCRIPTION OF THE DRAWING
[0006] The foregoing and other objects of the present invention may
become more apparent from a reading of the ensuing detailed
description together with the drawing in which:
[0007] FIG. 1 shows a prior art method of vertically stacking an
array of laser diodes each mounted on a respective microchannel
heat sink;
[0008] FIG. 2 shows an enlarged view of FIG. 1 modified so that the
fluid paths are aligned but requiring custom built microchannel
heat sinks;
[0009] FIG. 3 is an isometric view of the manifold of the present
invention having fluid paths lengthened to reduce corrosion of the
copper microchannel heat sinks; and
[0010] FIG. 4 shows the manifold of FIG. 3 assembled with its array
of microchannel heat sinks.
DETAILED DESCRIPTION
[0011] FIG. 1 shows a vertical stack of microchannel heat sinks 10
each having an end-mounted laser bar 15 according to the '043
patent. End-mounting of the laser diode bars 10 allows the distance
q between adjacent emitted light beams 16 to be smaller than the
distance p between the center lines of adjacent heat sinks whereas
mounting the laser diode bars on the top surface of each of the
heat sinks determines that the distance q can be no smaller than
the thickness of the heat sink. While the prior art arrangement of
FIG. 1 allowed the light beams emitted by the laser diode bars to
be more closely spaced, mounting the laser diode bars at the end of
the microchannel heat sinks was not very efficient from the
standpoint of cooling.
[0012] Unfortunately, identical microchannel heat sinks cannot be
used in the configuration of FIG. 1 because, as shown, the cooling
water inlets 14 and outlets 15 do not line up. This requires either
that microchannel heat sinks with differently positioned inlets and
outlets be used, as in FIG. 2, or that intermediate connectors be
used between the heat sinks to connect the cooling water paths. It
should be noted that in FIG. 2 it is necessary to use an insulating
layer 27 between adjacent heat sinks 20 and it is also necessary to
use an insulating standoff layer 26 between the "+" terminal 24 and
heat sink 20.
[0013] The current path may be traced from the positive supply over
connector 25 to positive terminal 24, wire jumper 23 to laser diode
21, copper heat sink 20, and connector strap 28 to the positive
terminal 24' of the next adjacent heat sink. 20'. Although only one
wire jumper 23 is shown, typically many are used. It should be
noted that in FIG. 2 the fluid path between adjacent heat sinks 20,
20' has a very short length L.
[0014] In previous designs of copper, microchannel heat sink arrays
little thought has apparently been given to the electrical
properties of the fluid path between adjacent heat sinks. Water is
the most common fluid used and water has conductivity. Even
de-ionized water flowing through the copper lined channels of the
heat sinks will eventually absorb copper ions leading to some
degree of fluid conductivity. The usual serial connection of
microchannel heat sinks, as shown in FIG. 2, determines that a
potential difference will exist between adjacent heat sinks 20, 20'
and, concomitantly, the fluid path within each heat sink will be at
a different potential. The fluid path then transports a "leakage
current" between the heat sinks. The resistance of this fluid path
is given by 1 R = L A ,
[0015] where L is the length of the fluid path between adjacent
microchannel heat sinks, .rho. is the resistivity of the fluid and
A is the cross-sectional area of the fluid path. Assuming, for
example, that the potential difference between adjacent
microchannel heat sinks produces a current of one milliampere in
the fluid path. One milliampere current in terms of electron flow
rate is: 2 N ( e - ) t = I e = 10 - 3 1.602 10 - 19 = 6.24 10 15
electrons per second .
[0016] Based on the crude approximation that each electron flowing
in the fluid path will be accompanied by one atom of copper the
rate of mass transfer through the fluid path is given by: 3 m t = m
atom N ( e - ) t .
[0017] If an atom of copper weighs 1.06.times.10.sup.-22 grams, the
rate of mass transfer of copper through the fluid path is, roughly:
4 m Cu t = ( 6.24 .times. 10 15 ) ( 1.06 .times. 10 - 22 ) 6.6
.times. 10 - 7 grams / sec .
[0018] Accordingly, in about one hour a current of one milliampere
will cause a few milligrams of copper to be transported through the
fluid path. Since the microchannel heat sinks are made of very thin
copper layers it is not surprising that failures have occurred in
the field. Increasing the length of the fluid path by a factor of
two or more will increase the resistance of the fluid path and
correspondingly reduce the leakage current through the fluid path.
It is an object of the present invention to provide an array of
copper microchannel heat sinks having a longer fluid path between
adjacent heat sinks to reduce the leakage current in the fluid
path.
[0019] An illustrative embodiment of a manifold 300 providing a
longer fluid path between adjacent microchannel heat sinks is shown
in FIG. 3. Manifold 300 is advantageously fabricated of
non-conductive material such a plastic. The top surface of manifold
300 provides a series of parallel offset plane surfaces 301-
through 301-6 each of which is dimensioned to accommodate a
respective copper microchannel heat sink. Advantageously, the
offset parallel planes are separated from one another by respective
alignment walls or ridges 302-1 through 302-5 to facilitate
accurate placement of the heat sinks. Each offset plane includes a
vertical fluid inlet channel 303 and a fluid outlet channel 304.
The fluid inlet channels between adjacent offset planes each have a
length L.sub.300 that is at least as long as the width of the
respective microchannel heat sink, a length which is a multiple of
the length L of FIGS. 1 and 2. The fluid inlet channels 303-1
through 303-6 are supplied through a common feeder channel 305
while the fluid outlet channels discharge into a common discharge
channel 306. Advantageously, each inlet channel 303 and outlet
channel terminates in an O-ring accommodating recess 307, 308 so
that a fluid tight seal can be made with the respective
microchannel heat sink.
[0020] Referring now to FIG. 4 there is shown the manifold 300
together with its associated copper microchannel heat sinks 400-1
through 400-6. Each heat sink mounts a respective laser diode bar
401-1 through 401-6 at its far edge. To simplify the drawing the
"jumper" wires leading to the laser diode bars, the standoff
insulators and the terminal on the insulators have been omitted but
are similar to those shown in FIG. 2. A series of flat, parallel
glass plates 404-1 through 404-6, each having a beveled edge 406-1
through 406-5 advantageously making a 45 degree angle with the axis
of the light emitted from the respective laser diode bar is
positioned to reflect each light output to the left, the separation
between the light output planes being no greater than the height of
the "riser" between adjacent steps (planes 301-1 through 301-6) of
manifold 300.
[0021] What has been described is deemed to be illustrative of the
principles of the invention. Further and other modifications will
be apparent to those skilled in the art and may be made without,
however, departing from the spirit and scope of the invention.
* * * * *